Field of the Invention
The present invention relates to an axial piston device in which a plurality of axial piston members such as a hydraulic pump and a hydraulic motor are accommodated in an oil-retainable housing.
Related Art
In axial piston devices in which a plurality of axial piston members are accommodated in an oil-retainable housing, lubrication of the plurality of axial piston members is generally carried out by immersing the plurality of axial piston members in oil retained in the housing, but this configuration is problematic in that the axial piston members all receive rotational resistance caused by the retained oil.
In order to address this problem, it is proposed that in a hydrostatic transmission in which a hydraulic pump and a hydraulic motor are both accommodated in an oil-retainable housing, with one of the hydraulic pump and the hydraulic motor being placed above the other, a drain port is provided in a place lower than the upper edge of the cylinder block of the hydraulic pump or the hydraulic motor, whichever is placed higher (see, for example, JP2001-059561A, hereinafter referred to as Patent Document 1).
Compared with the configuration in which the hydraulic pump and the hydraulic motor are completely immersed in retained oil, the hydrostatic transmission described in Patent Document 1 is effective in being capable of reducing rotational resistance to the hydraulic pump and the hydraulic motor resulting from retained oil while lubricating the hydraulic pump and the hydraulic motor.
However, in the configuration described in Patent Document 1, the hydraulic motor, which is the lower of the hydraulic pump and the hydraulic motor, is completely immersed in retained oil, and a part of the hydraulic pump placed higher is also immersed in retained oil.
Therefore, there is still room for improvement from the viewpoint of reducing rotational resistance to the hydraulic pump and the hydraulic motor resulting from retained oil.